The present invention relates to an aluminum alloy propeller shaft as a power transmission device for a vehicle, and a friction welding process of the propeller shaft.
As is generally known, a method of bonding a tube of a vehicular propeller shaft and a yoke member to each other includes a friction welding process with high accuracy in addition to MIG or TIG welding.
In the friction welding process, a yoke member as one member is brought into friction contact with each of opposite ends of a tube as the other fixed member while being rotated through a main shaft. Then, in a preheat step, the members are pressed onto each other at a predetermined preheat pressure to thereby cause a temperature rise thereof up to a predetermined temperature value in order to obtain an amount of heat necessary for pressure welding the members. Subsequently, a rotation number and a friction pressure of the main shaft are set at predetermined values to heat a bonding interface between the members up to a temperature necessary for friction welding.
After that, in a stage in which the friction step is completed, the rotation of the main shaft is stopped and transition to an upset step is carried out with a preset upset delay time. In the upset step, by using an upset pressure, an oxide and a heat-softened portion present on the bonding interface between the members are removed as a flash to an outside, and solid-phase welding of fresh surfaces of the members is carried out. In a case where the upset pressure is low, removal of the oxide cannot be sufficiently attained. On the other hand, in a case where the upset pressure is high, there occurs plastic deformation or crack in the weld portion at which the members are welded to each other, thereby causing deterioration in welding quality. Therefore, the upset pressure is appropriately regulated in relation to the friction pressure.
Further, the preheat step and the friction step are managed by a timer, and carried out for a period of time from start of the preheat step to stop of rotation of the main shaft. The upset step is also managed by a timer, and carried out for a period of time which starts from the stop of rotation of the main shaft and terminates at a predetermined time. Within the upset time, upon a changeover from the friction pressure to the upset pressure, the upset delay time is set to control heat input to be applied to the members in the friction process and a heat influence range of the members, and transition to the upset step is carried out.
Japanese Patent Application Unexamined Publication No. H11-156562 A discloses such a friction welding process.